1. Field of the Invention
The present invention relates generally to a polyaniline/c-MWNT nano-composite, and more particularly, the present invention relates to a polyaniline/c-MWNT nanocomposite which could be used for electromagnetic shielding or anti-static shielding.
2. Description of the Prior Art
As electronic devices are designed smaller and smaller with higher and higher density, electronic devices are disturbed more and more seriously by electromagnetic waves and radiation frequency. Therefore, the electron-magnetic compatibility of an electronic device is always concerned while fabricated, stored, transported and operated. Because electronic devices are broadly applied to various fields including the people's livelihood, the national defense and even the space industry, etc, how to avoid the disturbance by electromagnetic waves and radiation frequency has become the gist of research.
Those electronic devices need avoiding the disturbance of electromagnetic waves and radiation frequency could adopt conducting shields to cut off the electromagnetic waves. When electromagnetic waves pass through the shields, the energy of electromagnetic waves would be reflected or absorbed and therefore the disturbance of the electromagnetic waves could be decreased. In conventional arts, conducting materials are electroplated or coated on plastic casing, or infilled in plastic casing for electromagnetic shielding. The method of electroplating to electroplate metals on casing has disadvantages of pollution, inconvenience in manufacturing, and high cost. Moreover, a metal shield has a problem of easy oxidation. A metal shield avoids the disturbance by means of reflecting electromagnetic waves, however, as for some other application fields such as national defense, electromagnetic waves should be shielded by means of absorbing them. On the other hand, the method of infilling conductive materials in plastic casing has problems such as bad efficiency of shielding and difficulties in recycling plastic casings. To summarize, a material with low pollution, high conductivity, microwave absorption, and capable of coated on a large area could solve the problems mentioned above.
Electromagnetic shielding effect is related to the absorbing and reflecting ability of a material. A metal shield has high density of free charge on its surface, so when electromagnetic waves incident the surface of a metal, most of the electro-magnetic waves will be reflected. Therefore, a metal shield avoids the disturbance by means of reflecting electromagnetic waves.
When electromagnetic waves incident a conductive high polymer, the conductive high polymer generates an induced current corresponding to the electromagnetic waves and transforms the electric energy to heat by means of the flowage of the induced current to deplete the energy of the electromagnetic waves. Thereby, a conductive high polymer could avoid the disturbance by means of absorbing electromagnetic waves. Among all kinds of conductive high polymers, the polyaniline, which is a material with high potential, has advantages of high conductivity, cheap raw materials, high stability, and easy fabrication.
Otherwise, the carbon nanotube has fine physical, mechanical, chemical, and electric characteristics as well as high stability, so it is widely applied to various fields. Moreover, a composite is composed of two or more materials with different material characteristics by means of physical or chemical combination, so the composite not only has better property than any one of the composition but also keeps every single material's origin characteristic. Practically, nanocomposite has become an important issue for researchers from all over the world because of its enormous potential. A composite including carbon nanotubes therein succeeds to the characteristic of the carbon nanotube, and it is supposed to have high value.
However, the carbon nanotubes tend to entwine each other owing to their own van der waals force. And also because the chemical stability, there is no functional groups on the surface of the carbon nanotube, so that they are difficultly dissolved or dispersed in organic solvent or water. The above-mentioned characteristics of carbon nanotubes are problems waiting to be improved.